AMPAR ligand discovery for Alzheimer's disease

项目摘要。AMPA受体(AMPAR)是快速谷氨酸能神经传递的主要转导分子 在整个中枢神经系统(CNS)中，它们控制兴奋性突触的强度并调节 长时程增强(LTP)--学习和记忆功能的基本机制。安培功能障碍 与多种神经退行性疾病有关，包括阿尔茨海默病(AD)。因此 AMPAR的药理调节代表了一种有吸引力的治疗方法。正电子发射断层摄影术 (PET)能够量化体内的生化过程，而合适的AMPAR配体将大大 加深对不同病理生理AD下AMPAR介导的离子型谷氨酸信号转导机制的认识 条件，否则无法通过体外(破坏性)分析。活脑组织中AMPAR的PET定量研究 将提供对新的AMPAR靶向的分布、靶向参与和剂量占用的评估 神经治疗学。到目前为止，还没有成功的例子为GluA2特定的AMPAR创建映像 药物发现和临床应用，代表着我们在体内研究这一靶点的能力的一个重大不足。因此， 我们建议开发一种新型的PET配体来填补这一空白，作为第一个翻译成像工具。 我们是第一批开发AMPAR GluA2特异性配体的团体，包括[11C]AMPA-1905(由 2020年的PI)。然而，由于体内边际结合的特异性，该配体被终止。在我们的第二代， 我们确定了一种铅分子，AMPA-2076，它比所有其他分子都显示出高的结合亲和力和良好的选择性 Iglu受体。合成了AMPA-2076的18F-同位素，初步的PET成像研究证实 我们已经克服了GluA2特异性AMPAR配体开发的两个主要障碍，实现了：1) 大大提高了大脑中的体内稳定性和2)高靶点特异性。虽然AMPA-2076是一款很有前途的 用于开发新的以GluA2为靶标的AMPAR配体的领先分子，进一步优化以改善结合 为翻译的跨物种成像研究寻找具有适当脑动力学的特异性以达到最佳 AMPAR(GluA2亚基)在活脑中的定量用于AD患者的药物发现和临床翻译。 在AMPA-2076作为药物化学优化的有效先导的基础上，作为具体目标，我们 将设计和准备可用11C或18F标记的GluA2特异性AMPAR调制器的聚焦文库， 并评估他们量化AMPAR活性和在啮齿动物和非人类药物挑战期间的变化的能力 灵长类动物，以及死后人脑组织的放射自显影和生物学验证。这件事的影响 工作不仅是开发出第一个成功的高亲和力和选择性的AMPAR PET配体，用于研究 神经退行性疾病相关的生物学过程，最终也是通过PET成像验证在较高 物种，以促进该配体的潜在临床翻译和监测新的神经治疗药物的靶向反应 治疗神经退行性疾病，包括阿尔茨海默病。

Project Summary. AMPA receptors (AMPARs) are the principle transducers of fast glutamatergic neurotransmission throughout the central nervous system (CNS), where they control the strength of excitatory synapses and modulate long-term potentiation (LTP) - a fundamental mechanism of learning and memory function. AMPAR dysfunction has been implicated in a variety of neurodegenerative diseases, including Alzheimer’s disease (AD). Therefore pharmacological modulation of AMPAR represents an attractive therapeutic approach. Positron emission tomograohy (PET) is capable of quantifying biochemical processes in vivo, and a suitable AMPAR ligand would substantially improve our understanding of AMPAR-mediated ionotropic glutamate signaling under different pathophysiological AD conditions, otherwise inaccessible by ex vivo (destructive) analysis. Quantification of AMPAR in living brain by PET would provide the assessment of distribution, target engagement and dose occupancy of new AMPAR-targeted neurotherapeutics. To date, no successful examples have been demonstrated to image GluA2-specific AMPAR for drug discovery and clinical use, representing a significant deficiency of our ability to study this target in vivo. Therefore, we propose to develop a novel PET ligand that can fill this void, as the first translational imaging tool. We are the first groups to develop AMPAR GluA2-specific ligands, including [11C]AMPA-1905 (developed by the PI in 2020). However, this ligand was discontinued due to marginal binding specificity in vivo. In our 2nd generation, we identified a lead molecule, AMPA-2076, which showed high binding affinity and excellent selectivity over all other iGlu receptors. An 18F-isotopologue of AMPA-2076 was synthesized and preliminary PET imaging studies confirmed that we have overcome two major obstacles for GluA2-specific AMPAR ligand development by achieving: 1) substantially-improved in vivo stability in the brain and 2) high target specificity. Though AMPA-2076 is a promising lead molecule for the development of new GluA2-targeted AMPAR ligands, further optimization for improved binding specificity with proper brain kinetics are sought for translational cross-species imaging studies to achieve optimal AMPAR (GluA2 subunit) quantification in the living brain for drug discovery and clinical translation for AD patients. On the basis that AMPA-2076 serves a validated lead for medicinal chemistry optimization, as specific goals, we will design and prepare a focused library of GluA2-specific AMPAR modulators amenable for labeling with 11C or 18F, and evaluate their ability to quantify AMPAR activity and changes during drug challenge in rodents and nonhuman primates, as well as autoradiography and biological validation in postmortem human brain tissues. The impact of this work is not only to develop the first successful high-affinity and selective AMPAR PET ligand for the study of neurodegenerative disease-related biological processes, but also ultimately, via PET imaging validation in higher species, to advance this ligand for potential clinical translation and monitor target response of novel neurotherapeutics for neurodegenerative diseases, including AD.